# What measure the length?

Under the length should be understood a physical quantity, which is a characteristic of the length of lines in numbers. This concept has several definitions that you should be aware of. Units, tools and instruments for measuring length are also different. Therefore, in this article we will describe how and how to measure the length.

## What is length

As we have said, the term length must be understood as a physical quantity. In the narrow sense of the word, it means size in the longitudinal direction. That is, the length can be called the distance between two points of an object as far apart as possible. However, it is important to note that this distance should be measured horizontally, not vertically, as in the case of height measurement.

In physics, the concept of length is equivalent to the term “distance”. It should also be noted that in the overwhelming majority of measurement systems, length is the basic unit of measurement by which the remaining units are established. In the international system of units, the unit of length is the meter.

## Length units

First of all, it is necessary to say about the metric system, which is still the most convenient because of its simplicity. It is based on the unit of measure meter, and the rest are multiples of ten from it. For example, a kilometer is 10 meters in a cube. Such a system greatly simplifies the calculations.

In Russia, a man was a measure of length for a long time. This can be judged by the name of the measures, including the span, elbow, sazhen, and others. A span is a measure corresponding to the distance between the index finger and thumb in an extended position, the elbow is the length from the clenched fist to the bend of the elbow, and the sazhen is from the end of the fingers of one hand to the end of the other.

Of the various works of literature, we also know such a unit of measure for distance as a mile. It corresponds to today's 1,066.8 m. In ancient Russia, versts were boundary and track. The former were used to measure land, the latter - distances or paths.

In England and America used other units. For a long time in Britain there were the following units of length:

- yard;
- mile;
- foot;
- inch.

The yard is not part of the international system of units and is equal to 0.9144 meters. The mile came from ancient Rome, where it was equal to a thousand double steps of a soldier.This unit is still used in a number of countries where the metric system of measures is not used. It varies in different countries. In England, it corresponds to 1.6 kilometers. The foot is also not part of the international system and corresponds to 0.3048 meters. Inch, which is used today in the United States and Britain, is equal to 2.54 centimeters.

In addition, there is also a maritime length measurement system, which is based on the unit of measurement - nautical mile. It is equal to the length of one minute of the arc of the terrestrial ellipsoid meridian. Its length is variable and depends on latitude. The international nautical mile corresponds to 1,852 meters.

## Length measurement tools

The simplest tool for measuring length is considered to be a ruler, which is a narrow plate. On it, as a rule, there are divisions corresponding to the unit of measurement. It can be millimeter, centimeter, inch, etc. In cartography and geometry, this tool is used only for the purpose of drawing straight lines. Other tools are used to measure distances, and ruler measurement is considered to be insufficiently accurate.

Another common tool for measuring the length of an item is a tape measure. It is a tape on a reel, which is wound into the body with a special mechanism. It also contains divisions in the form of strokes in accordance with the unit of measurement. The most common roulettes are 3 or 5 meters long. However, there are also tools that can measure the length of up to 100 meters.

A measuring tool is a tool for measuring internal and external dimensions. It consists of two measuring surfaces, in the middle of which a size should be established. The main types of gauge are gauge, caliper, gauge and gauge. You can read more about the caliper in our article on How to use a caliper.

It should also be said about the end measure of length, which is often referred to as KMD. It is an exemplary measure of length (0.5-1000 millimeters), which is made in the form of a circular cylinder or a rectangular parallelepiped. The end measure of length is designed to store and transfer units of length.It is with its help that the check and the establishment on the size of measuring instruments occur.

## Distance measuring instruments

The so-called rangefinder is a device for determining the distance from the observer to a specific object. Range finders are active and passive. The former include laser, sound and light range finders, and the latter include instruments using object matching for a particular sample or optical parallax.

Separately, you should talk about such a device as a radio range finder. It helps to determine the distance using radio waves. This device is used in military, in space and air navigation and in other areas. This device sets the time during which the radio wave travels from it to a specific object and back. Thus, the distance to this object is directly proportional to the time interval.

By the method of measurement, such devices are divided into pulsed radio range and phase. In the first case, the measurement of the delay time of the reflected signal is carried out, while in the second, the number of wavelengths that fit in the signal path is determined.

It is important to add that very small distances are usually measured with the help of so-called measuring microscopes. A very large set of satellite and radio navigation systems for measuring length.

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